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Interfacing formats are selected from the Setup Menu, described on page 67. The
input/output lines on your GPS III are RS-232 compatible allowing easy
interface to a wide range of external devices, including PCs, differential
beacon receivers, marine autopilots and/or a second GPS receiver.
The NMEA 0183 version 2.0 interface format is supported by the
GPS III and enables the unit to drive up to three NMEA devices:
NMEA 0183 version 2.0 Approved sentences:
GPGGA, GPGLL, GPGSA, GPGSV, GPRMB, GPRMC, GPRTE,
GPWPL, GPBOD
Proprietary sentences:
PGRME (estimated error), PGRMM (map datum), PGRMZ
(altitude), PSLIB (beacon receiver control)
DGPS (Differential GPS) corrections are accepted in RTCM SC-104
version 2.0 format through the Data In line. The GARMIN GBR 21 is
the recommended beacon receiver for use with the GPS III. Other beacon
receivers with the correct RTCM format may be used, but may not correct-
ly display status or allow tuning control from the GPS unit.
The GPS III may be hard-wired to a vehicle’s electrical system (10-32
VDC) using an optional power/data cable. Consult the wiring diagram to the
right for proper connections. (The male connector on the back of the GPS
III is illustrated.) A cigarette lighter adapter is also available to power your
GPS III without making permanent connections.
Additional cables are available to connect your GPS III to a PC-compat-
ible computer’s serial port (PC Interface Cable) or to connect to a second
GPS III (Data Cross-Load Cable). Contact your GARMIN dealer for any of
these accessories.
78
APPENDIX C
Wiring / Interfacing
GARMIN
GBR 21
(+) Power
(-) Ground
Data In Data Out
GPS III Connections (from back of unit)
GARMIN GBR 21 Beacon Receiver
GPS III A 7/21/98 8:52 AM Page 78